6.2 Hellfire Citadel - Mythic Hellbreach

This page is to be a brief summary on the first three mythic boss fights of Hellfire Citadel, written from the perspective of a hunter. The purpose of this is to act as a documented archive of our kills and to potentially aid any others currently working on the boss who're looking for resources and happen to come across the page.
As of writing this post Might is at 11/13M and the first three bosses have been killed 7 times each - thus this is written both from the perspective of first time kills, as per the videos included, and also from the perspective of farm.

First boss is HELLFIRE ASSAULT

First kill was July 1, 2015 - world 48, US 25

Assault is a massive priority target gauntlet in the form of several convenient waves of trash that all come to you. And while this fight is a massive joke to us now, the reality is we finished our first kill by the skin of our teeth. Part of this was us not running the boxes in until last minute.
There are several classes who will do AoE clean up much better than you will, so focus pooling and lining up barrage / explosive traps isn't as important as focus pooling for berserkers, terrors and artilleries. Assault is an encounter where you will have to make hard decisions on what the current priority target is: felcasters? berserker? artillery? Or can you really get away with barraging those dragoons?

Marksmanship plays a lot differently than how it used to: no longer are you monitoring steady focus uptime or master marksmanship procs in a priority rotation that has an opener over a minute long - instead it's far more opportunistic. Marks hunters differentiate their damage between each other based on how well, and how quick, they swap to snipe targets above 80% for Aimed Shot Careful Aim, targets below 35% for Kill Shot Execute, and targets in cleave range of Chimaera Shot. The main opportunity you'll get in Assault is the chance to Chimaera cleave the first two artilleries as they roll through the gates toward the raid.
One of the things I focused on improving for our first kill was this new opportunistic play style, and it's something you should see in the video below despite my lack of 4p and hardcasting aimed: I prioritize swapping to berserkers, who at the time proved a small benchmark. There are many times where I made the choice to stay focused on the berserker despite the opportunity to swap to an above 80% felcaster or flamebelcher.

That's about it. For our raid I had to focus heavily on berserkers, swapping to terrors above all else - with as much controlled pushes as feasibly possible - and crank out artilleries. You'll notice that I actually swap sides from the left to kill an artillery on the right while the left only had a flamebelcher... An artillery that probably wouldn't have died if not for my doing so with stampede. What you have to focus on for your raid will depend on your own raids current benchmarks.
Oh, yeah, and as we're falling apart at the end.. Lack of control on the berserkers, the tanks - we realize all we freakin' had to do was run the dumb boxes in.

Second boss is IRON REAVER

First kill was July 2, 2015 - world 83, US 31

Iron Reaver is a fairly simple fight from a hunter perspective. Watch your range finder to stay spread out when you need to, be in range of healers, save barrage for bombs. Then it's just a matter of prioritizing Quick Fuse > Burning > Reinforced bombs during the air phase. Chimaera Shot on overlapped bombs and Barrage are really good for this. You can also get some good FelStorms in from a mirror trinket if you're lucky, but I believe many folk tend to swap the trinket out for this one.

The only thing you must absolutely avoid is being hit by barrage. You will die. Ranged always misjudge the cone. Keep your /stopcasting x2 macro on disengage so you can emergency maneuver out of a barrage you've misplaced yourself on. Barrage will only target healers, so watch their trajectories. Blitz is less dangerous, because if you see Reaver coming towards you then you can cast Deterrence and survive - assuming you strafe out of the second Blitz and do not take fire stacks.

Speaking of fire stacks, they're easily avoided. During pounding they will move outward from the boss, so just position yourself so fire that is travelling backwards does not travel over you.

Third boss is KORMROK

First kill was July 8, 2015 - world 183, US 43

Kormrok is also pretty simple, especially with an addon to map your place for soaking. Most folk are using Exorsus Raid Tools for this. Hold your cooldowns at the start or your stampede pets will run into the pool and die. You'll also most likely be out of range for the duration anyway.

Pop runes by facing your character in the direction you want to push them. Push enhanced runes together to get rid of them - do it fast and efficiently, deterrence is useful for this. Folks biggest mistake with runes is just trying to run over them fast, with no consideration for how many runes are left or where they are. The goal is to push them together so they despawn until there is only one left, then stomp it out too.

The order the abilities come will depend on your guilds strategy, but you can and should save barrage for hands, cleave Chimaera whenever possible (to small hands or to the tank hand) and don't stand where you should not be. Watch the range finder for pound, weave through blobs, or disengage if necessary. Don't stress too much about hand damage, since it's not overly your job - there are better classes who you will be relying on burst AoE for more.